It is estimated that approximately 50% of all cancer patients will undergo some form of radiation therapy as part of their curative treatment. The objective of radiation therapy is to accurately focus lethal doses of ionizing radiation to cancer cells while minimizing dose to healthy tissues surrounding the cancer. Towards that end there have been many technological innovations over the years to improve the accuracy of radiation therapy including better patient immobilization devices, computerized treatment planning based on three dimensional CT and MRI images and precise beam shaping through such devices as the multi-leaf collimator. Advance treatment techniques such as Intensity Modulated Radiation Therapy (IMRT) have enabled treatment “safety margins” surrounding tumors or “planned treatment volumes” to be dramatically reduced. Tumor motion as a result of patient breathing or cardiac function in such areas as the lungs or mediastinum may compromise the accuracy of delivery.
One solution to this problem is to increase the treatment volumes to account for the target drift. Other techniques involve modeling the motion as part of the treatment plan and gating or synchronizing the delivery with the target motions.
There exists today a need to assess and measure the various methods being employed to correct for errors in dose delivery to dynamic targets.
Navarro U.S. Pat. No. 6,225,622 to Navarro discloses a dynamic radiation scanning device wherein the entire phantom, along with any embedded radiation detector, is moved as a whole to asses beam flatness and uniformity.
Another prior approach involves intermittently moving a detector to various positions through a water-filled tank, and taking still (i.e., non-moving) radiation dosage readings at each position. This prior approach does not contemplate continuous movement of the detector relative to a fixed medium, and taking dosage readings while the detector is moving.
U.S. Pat. No. 6,697,451 to Acharya et al discloses a dynamic phantom an method for evaluation of calcium scoring. In the Acharya et al device, the center section of a phantom is moved to mimic cardiac motion for CT scoring of coronary calcification. This prior device does not provide for insertion of a continuously moving detector within a target volume.
Yang et.al (“An Investigation of tomotherapy beam delivery”, 1997, Medical Physics, American Association of Physics and Medicine) discloses a phantom positioning device wherein said device uses linear and rotational motions but to move an entire phantom linearly and rotationally as a whole, but does not disclose or teach movement of a target volume within the phantom.
Jiang et al (“An experimental investigation on intra-fractional organ motion effects in lung IMRT treatements”, 2003, Physics in Medicine and Biology, Institute of Physics Publishing) disclose sinusoidal movement of an entire phantom and its surrounding structure, similar to Yang, but does not disclose or teach moving a target within a structure.
Hugo et al (“The effects of tumor motion on planning and delivery or respiratory-gated IMRT”, 2003, Medical Physics, American Association of Physics and Medicine) disclose moving the entire phantom as with Yang and Jiang, and additionally discloses moving the phantom in a vertical and longitudinal direction simultaneously, but does not disclose or teach moving a target within a structure.
Sawada et al (“A technique for noninvasive respiratory gated radiation treatment based on a real time 3D ultrasound image correlation: A phantom study” 2004, Medical Physics, American Association of Physics and Medicine) disclose Targets embedded in a rubber cylinder that moves within a water tank simulating a human abdomen, for evaluation and development of 3D ultrasound system used to correct for respiratory tumor motions specific to the abdominal cavity. Sawada et al do not disclose or teach a thorax- or lung-simulating phantom, nor the provision of detectors within the target volume to assess dosage.